Efficacy of ivermectin against cutaneous Draschia and Habronema infection (summer sores) in horses.

The research article examines the effectiveness of using ivermectin as a treatment for summer sores, a skin infection in horses caused by Draschia and Habronema larvae.

Methodology and Results

• The study was conducted during the summer of 1980 on 31 horses naturally affected with summer sores. To evaluate the therapeutic effect of ivermectin, an initial biopsy was taken from 25 of these horses, and larvae of either Draschia and/or Habronema were found in 84% of these samples.
• The horses were treated with a single dose of ivermectin delivered intramuscularly at a dosage rate of 0.2mg of ivermectin per kilogram of the horse’s body weight.
• Seven days after the treatment, clinical improvement was observed in 84% of the horses. Their summer sores were replaced by healthy pink granulation tissue, which eventually healed completely within 1 to 5 weeks post-treatment.
• To measure the efficacy of the ivermectin treatment, the researchers performed another biopsy on 21 horses 1 to 6 weeks after the ivermectin treatment. In 86% of these samples, no larvae were found, indicating that the ivermectin successfully cleared the infection in the majority of cases.

Reinfection and Additional Treatment

• Despite the high success rate, 5 out of the 31 horses did not respond well to the single-dose ivermectin treatment. Larvae were found in biopsy samples taken from 3 of these horses 2 to 4 weeks after initial treatment, suggesting that these horses had been reinfected.
• However, these cases were successfully treated after the administration of a second dose of ivermectin. The biopsy samples from these horses became negative for larvae and their sores healed within 1 to 2 weeks following the second treatment.

Histopathological Analysis

• The researchers also conducted histopathologic examination of biopsy sections taken from the horses both before and after the ivermectin treatment. Before treatment, these sections showed granulation tissue (the new connective tissue that forms on the surfaces of a wound during the healing process) with significant infiltration by eosinophils (a type of white blood cell that fights off parasites), multiple eosinophilic abscesses (pockets of pus), and sections of nematodes (parasitic worms).
• Post-treatment histopathological examination showed a marked decline in the number of eosinophils and the absence of eosinophilic abscesses and nematodes. The granulation tissue appeared to have matured, as evidenced by the presence of dense fibrous connective tissue.